Predicting hardness of dense C3N4 polymorphs

Abstract

We report the calculations of the Vickers hardness of five predicted C3N4 polymorphs by using the microscopic model of hardness. The hardest phase, cubic C3N4, has the hardness of 92.0GPa, softer than diamond, although its modulus is higher than that of diamond. The densest phase, cubic spinel C3N4, has the lowest hardness of 62.3GPa in the five polymorphs. Our analysis suggests that the hardness of simple-structured covalent materials might not exceed that of diamond.